This invention relates to a fastener for fastening two panels as opposed to each other across a fixed space by simple manipulation.
The fastener which is used for fastening an interior decorative board (trim board) to a body panel across a narrow intervening space in an automobile or the fastener which is used for fastening a printed circuit board or other similar board to a chassis across a space in an electric appliance comes in a variety of designs. As one typical version of the fastener of this principle, there may be cited what is generally known as a screw grommet. The screw grommet comprises a shank of a non-circular cross section adapted to expand radially by the insertion of a screw into a socket bored in the shank and a flange formed at the upper end of the shank. The use of this screw grommet is accomplished by forming in a supporting panel a through hole exactly conforming to the cross-sectional outline of the shank of the screw grommet, inserting the shank through this hole until the flange comes into intimate contact with the surface of the supporting panel, then applying fast to the upper surface of the flange a supported panel having bored in advance therein a hole for permitting insertion of the aforementioned screw, and helically driving the screw through the screw hole of the supported panel into the shank of the grommet. The helical insertion of the screw causes the shank to expand radially and secures the grommet in position so fast that it may not come off the supporting panel. Consequently, the supported panel in which the screw has been inserted is fastened to the supporting panel as separated by a distance equalling the thickness of the flange. The removal of the supported panel can be accomplished by rotating the screw in the opposite direction. (U.S. Pat. Nos. 3,869,958, 3,933,076 and 4,070,945).
The grommet of the construction described above inevitably necessitates a troublesome operation of helically driving the screw. With a view to enhancing the efficiency of work involved in actual use, there has been developed an improved grommet designed to obviate the necessity of helically driving a screw. Generally, the improved grommet has a plurality of protuberances formed in the shape of lines or dots on the inner surface of the screw socket bored into the shank. With this grommet, the fastening of two panels is effected by forcing the screw straight into the socket in the shank, so that the threads of the screw may ride over the protuberances and keep them elastically pushed backwardly to attach the supported panel fast to the supporting panel. Once the two panels are fastened as described above, the protuberances on the inner surface of the screw socket are engaged with the threads of the screw fast enough to prevent the screw from slipping off the screw socket. Thus, the two panels remain in fast union. For the separation of the panels, the removal of the screw from the screw socket is accomplished by reversely rotating the screw against the screw socket.
The fastener capable of providing fast union of two panels by simple depression of a screw makes the work of fastening the two panels easy. The known fastener of this type, however, is not free from disadvantages. When it is put to use, for example, a special tool is an absolute necessity. Moreover, since the screw during its depression into the socket causes no perceivable tactile sensation to the user, the extent to which the screw is depressed is variable from one user to another and, accordingly, the condition of the union consequently established between the two panels is open to personal error.